Simple Question about Resultant Force and Direction in Statics

[Marioqwe]

Homework Statement

http://img11.imageshack.us/f/screenshot20110117at120.png/

The question is 2.3

Homework Equations

Law of cosines and law of sines.

The Attempt at a Solution

I used the law of cosines to find the resultant force. It is 139.1 lb. However, I get 113.1 degree for the direction of the resultant force. The textbook says that it is 67 degrees. I noticed that I get 67 degrees if I subtract 139.1 from 180 degrees. Why is this? Also, I am a little confused about significant figures. Why are they giving only two sig figs for the direction?

Thanks

 

[nvn]

Marioqwe: Usually you give the vector direction measured from a horizontal axis. Try that. They might be listing only two significant digits because the question asks you to determine the answer graphically, which is a less precise method than a calculator. Anyway, the correct answer is 67.0 deg, which rounds to the same answer.

 

[Marioqwe]

Thank You for your reply. It is more clear now.